The invention relates to a hydraulic valve control device for a stroke valve for an internal combustion engine.
German Patent Document DE 3,836,725 C1 already discloses a hydraulic valve control device for a stroke valve, particularly for arrangement in an internal-combustion engine. A valve stem of the stroke valve is connected to a piston which separates two stroke spaces in a cylinder from one another which can each be connected to a pump for working fluid or to a reservoir via inlet and outlet ports capable of being covered by the piston. In order to lower the energy requirement of the actuating arrangement, the two inlet ports open in a middle actuating region of the piston are directly connected to one another by means of a conduit. Two oppositely acting compression springs engage on the piston or valve stem and, in equilibrium, hold the piston in a middle position with respect to its two end positions, as a result of which the valve is partially opened when the working fluid expands or when the internal-combustion engine is at a standstill.
In devices of the relevant generic type, valve pockets are provided in the piston by means of the valve which is partially opened in the non-actuated position of rest, or additional tension devices keeping the valve closed in the non-actuated position of rest are required.
An object on which the invention is based is to improve further a hydraulic valve control device of the relevant generic type.
This object is achieved according to the invention by providing a hydraulic control device for a stroke valve, which valve control device is arranged particularly in an internal-combustion engine, the stroke valve comprising a valve stem and a first spring acting on the valve stem in a valve-closing direction as well as a second spring acting at least periodically on said valve stem in a valve-opening direction, the valve stem being connected at least to a control piston which is arranged in a working space and can be loaded on two sides with a working fluid and by means of which, in a region of its end positions, in each case a pressure space belonging to the working space and separable hydraulically from the working space is partially limited, a pressure of the working fluid in the working space being regulatable via a pressure source together with a switching valve and a supply conduit and, in a region of at least one of two end positions of the control piston, the pressure space assigned to said at least one end position is capable of being relieved of pressure via a connecting duct, wherein the prestressing force of the second spring can be regulated while the valve control device is in operation and, with the working fluid relieved of pressure in the working space and with the second spring contracted, the first spring holds the stroke valve in a closed position.
One advantage of the device according to the invention is that the stroke valve is closed in the non-actuated position of rest. Thus, valve pockets in the piston or separate tension devices keeping the stroke valve closed in the non-actuated position of rest can be dispensed with.
In comparison with electromagnetic valve control devices, the hydraulic device according to the invention also has inter alia fundamental advantages, since heavy, large-size electromagnets necessitating high currents for the purpose of applying the corresponding control forces are dispensed with. In the valve-actuating device according to the invention, no consumption of pressure oil occurs during the valve movement, but only a relatively small internal stream of blind oil flows, this being advantageous particularly with regard to the valve control times and the energy consumption of the device. The supply of energy takes place automatically, predominantly in the closed position of the stroke valve.
A further advantage of the device according to the invention is that operations of catching and holding the stroke valve take place automatically. An excessive force for overcoming the gas forces in the cylinder of the internal-combustion engine (pushing-open work by the stroke valve) can be controlled via the pressure level of the oil-pressure spring.
If the valve drive and the oil-supply bores are integrated into the cylinder-head structure, the radial overall space can be reduced to such an extent that a diameter of only approximately 25-30 mm is needed for each hydraulic unit. Since the entire cam mechanism is dispensed with, a reduction in the overall space requirements for the valve mechanism is thus achievable.
One advantage of the variation in the prestressing force of the second spring in certain preferred embodiment is that on the one hand, the energy loss occurring essentially as a result of friction during the actuation of the device can be compensated by a retensioning of the second spring and, on the other hand, a reliable closing of the opened valve is achieved, in that a possibly excessive remaining prestressing force of the second spring can be reduced, so that the force of the first spring can reliably execute the closing movement.
In certain preferred embodiments, the second spring is an oil pressure spring, the oil pressure of which is controllable. In other preferred embodiments, it is contemplated to use a helical spring or the like instead of the oil-pressure spring, in which case the spring articulation point is, for example, cyclically displaceable, so that the prestressing force of this spring can be adjusted while the device is in operation. This can be carried out, for example, by means of hydraulic force transmission.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.